The present application is generally related to the field of scanning probe microscopy (SPM) techniques such as scanning tunneling microscopy (STM). The invention of SPM techniques has revolutionized the study of nanoscale and atomic scale surface structures and properties. SPM has been a particularly useful tool for studying surfaces and new two dimensional (2D) materials such as graphene and topological insulators. In a typical application, a scanning probe is controlled by a SPM controller to scan across the surface of a sample material along x- and y-directions in order to produce a raster scan image. The total area of the scan image corresponds to the total scan area of the scanning probe over the sample surface. In some SPM applications, each pixel of the scan image comprises signal intensity that may correspond essentially to the sample height signal in the z-direction at each location along the scan path of the scanning probe tip, such that the produced scan image represent a topographical image. The nature of the signal intensity recorded in each pixel of the scan image depends on the interaction model of the scanning probe tip with the atoms of the sample surface.
In the case of STM, the magnitude of a tunneling current between the conductive STM probe tip and the atoms on the sample surface is a sensitive function of the distance between the STM probe tip and the sample surface. Therefore a topographical height image of the sample surface inside a scan area can be produced by the STM controller based on the probe current at each location of a raster scan path.
Recently, applications of SPM techniques in materials science research have extended from mapping precise surface topographical information to mapping physical properties such as measurements of surface potential, electric polarization, magnetization etc.